Changes

#5022 : Cleanup ServletHandler, specifically with respect to making filter chains more extensible
#5368 : WebSocket text event execute in same thread as running binary event and destroy Threadlocal
#5378 : Filter/Servlet/Listener Holders are not started if added during STARTING state.
#5409 : HttpClient fails intermittently with "Invalid response state TRANSIENT"
#5417 : Badly configured HttpConfiguration.securePort can lead to wrong port produced by ForwardedHeader
#5443 : Request without Host header fails with NullPointerException in ForwardedRequestCustomizer
#5451 : Improve Working Directory creation
#5454 : Request error context is not reset
#5475 : Update to spifly 1.3.2 and asm 9
#5480 : NPE from WebInfConfiguration.deconfigure during WebAppContext shutdown

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